The Quinone outside Inhibitor (QoI) group of fungicides†, which includes the strobilurins, are among the most extensively used fungicides in cereal production. Following their introduction in the late 1990’s, resistance to mildew in wheat developed very rapidly. Recently, the mutation responsible for resistance has also been found in Septoria tritici, the most widespread disease in wheat. Although there are no confirmed reports that this has resulted in control failures in the field, this finding indicates that resistance to the QoI fungicides may develop in Septoria and potentially in other diseases.
Resistance management strategies have been in place since the strobilurins were first introduced. In cereals, these include restricting usage to two applications and, where possible, using in mixture with other fungicides that have a different mode of action. It is known that around 20% of cereal growers are applying three or more applications of QoI’s and are thus not following the existing resistance management guidelines.
If widespread practical resistance were to develop to major diseases such as Septoria this could have serious implications for disease control in affected crops, and would render some groups of fungicides ineffective. Thus it is important to minimise the likelihood of resistance developing. This can be best achieved by the implementation of an effective resistance management strategy in cereals as well as in other crops. New resistance management guidelines for cereal use have recently been proposed by the International Fungicides Resistance Action Committee ( FRAC) and the UK Fungicides Resistance Action Group ( FRAG-UK). These go further than previous guidelines, and involve the following key points:
- In cereal crops the number of QoI containing sprays must not exceed two.
- QoI products not already containing another active substance must always be used in mixture with a product containing another active substance that is not from the QoI group and is recommended for control of the same disease.
- QoI products should be used preventatively or as early as possible in the disease cycle. They must not be relied on for curative ability.
The full management strategy is available from FRAG-UK.
It is vitally important that all users of QoI fungicides adhere to the latest resistance management guidelines. Management strategies for other crops are also available from both FRAG-UK and FRAC. These are similar to those for cereals in limiting the number of QoI containing sprays to a proportion of the total number of applications normally applied and recommending application preventatively or early in the disease cycle. PSD is currently considering whether any statutory action is necessary to support the resistance management guidelines for this group of chemicals.
† QoI active substances currently registered in the UK are azoxystrobin, famoxadone, fenamidone, kresoxim-methyl, picoxystrobin, dimoxystrobin, pyraclostrobin and trifloxystrobin. They were previously known as STAR (Strobilurins And Related compounds) fungicides.
